1. Field of the Invention
The present invention relates to a method of writing a figure visible to the naked eye, such as a character, picture, and the like, on an optical disk, and an optical disk suitable for such method.
2. Background Art
Major features of optical disks include the fact that the recording medium (disk) can be removed from the recording/reproduction unit and that the recording medium is inexpensive. The user can remove the medium from the unit and affix a label or write characters on it with a pen in order to indicate the recorded content and distinguish from other disks. Since such labels or written characters and the like are on the upper-most surface of the disk, they tend to become soiled or peeled during handling, resulting in a difficulty in reading them and a soiled appearance.
Various display technologies have been proposed to replace the aforementioned labels or written characters, as disclosed in JP Patent Publication (Kokai) No. 2003-016649 A, ISOM/ODS2005 Technical Digest, MA4 (LightScribe), and “Joint Development of ‘Labelflash™ Technology’ to Enable Writing on Disk Label Surface Using Data Recording Laser of a Recordable DVD Drive” (2005.10.19): http://www.fujifilm.co.jp/news_r/nrj1423.html. These technologies enable the drawing (writing) of characters or pictures using changes in reflectivity in the small-sized bits recorded in an optical disk which are not visible to the naked eye but which are visible when a large number of them are gathered. JP Patent Publication (Kokai) No. 2004-171605 A discloses a technique involving a diffraction grating in which a change in color depending on the angle of view is utilized.